Valgrind 发现了 3 个内存泄漏，但我不知道它们在哪里

Question

我尝试自己实现基本字符串 class，它工作正常，但 Valgrind 说有 3 处内存泄漏，我无法弄清楚泄漏的位置和原因。我真的试图删除不再使用的所有内容（我今天开始使用 Valgrind）。现在我真的很关心我的基本 C/C++ 内存管理知识。我对代码中 Valgrind 发现泄漏的地方进行了评论 (//VALGRIND)。我还上传了此错误消息的屏幕截图 click to see the screenshot.

编辑：我更新了截图，所以你可以看到完整的输出。

StringT.h

template<typename char_type = char>
class StringT {
public:

 explicit StringT(const char_type *str) {
        if (str != nullptr) {
            size_t len = strlen(str);
            m_str = new char_type[len + 1]; //VALGRIND: 6 bytes in 1 blocks are definitely lost in loss record 1 of 3
            strcpy(m_str, str);
        }
    }

   ~StringT() {
        delete [] m_str;
    }


StringT(const StringT & other) {
        size_t len = 0;
        if (other.m_str) len = strlen(other.m_str);
        m_str = new char_type[len + 1]; //VALGRIND: 6 bytes in 1 blocks are definitely lost in loss record 2 of 3
        strcpy(m_str, other.m_str);
    }

    StringT(StringT && other) noexcept {
        m_str = other.m_str;
        other.m_str = nullptr;
    }


     StringT & operator+=(const StringT &other) {
        if (other.m_str == nullptr) //when other str is empty just return current Str
            return *this;

        const size_t mysize{m_str ? strlen(m_str) : 0}; // check if not null then call strlen
        const size_t osize{other.m_str ? strlen(other.m_str) : 0};

        char *newStr = new char_type[osize + mysize + 1]; //VALGRIND: 11 bytes in 1 blocks are definitely lost in loss record 3 of 3
        newStr[0] = '[=10=]'; //strcat searches for '[=10=]', so newStr has to be a valid String

        if (m_str) strcat(newStr, m_str);
        if (other.m_str) strcat(newStr, other.m_str);

        delete[] m_str; //delete old string
        m_str = newStr; //set member to new concatenated str

        return *this;
    }

    size_t length() const {
        if (!m_str) return 0;
        return strlen(m_str);
    }


    friend
    std::ostream &operator<<(std::ostream &out, StringT<> &other) {
        if (other.m_str) out << other.m_str;
        return out;
    }

private:
    char_type *m_str{nullptr};
};

main.cpp

int main() {

    const char *cArr = "Hello";
    const char *cArr2 = "World";
    StringT<char> hello(cArr);
    StringT<char> world(cArr2);
    StringT<char> emptyStr;

    std::cout << "hello: " << hello << std::endl;
    std::cout << "world: " << world << std::endl;
    std::cout << "emptyStr: " << emptyStr << std::endl;

    StringT<char> hCopy(hello);
    StringT<char> wMove(std::move(world));

    std::cout << "hCopy: " << hello << std::endl;
    std::cout << "hCopy: " << hCopy << std::endl;
    std::cout << "world: " << world << std::endl;
    std::cout<<  "wMove: " << wMove << std::endl;
    std::cout<<  "lenMove: " << wMove.length() << std::endl;
    std::cout<<  "lenEmptyStr: " << emptyStr.length() << std::endl;

    hello += wMove;
    std::cout<<  "hello += world: " << hello << std::endl;

    return 0;
}

Answer 1

您的删除在这里：

StringT() {
    delete [] m_str;
}

但那是构造函数，不是析构函数。

Answer 2

正如已经回答的那样，delete 需要在析构函数中。但是，解决您的问题的正确方法是在这种情况下不要手动进行内存管理。您应该为您的 m_str 成员使用 std::unique_ptr：

std::unique_ptr<char_type[]> m_str;

这使您不必手动 new 和 delete。这也有助于在出现异常时防止内存泄漏。即使您 delete 分配了所有内容，如果在 new 和 delete 之间发生异常，您仍然会发生内存泄漏。 unique_ptr 有助于防止此类泄漏。

您的 class 只需稍作改动：

template<typename char_type = char>
class StringT {
public:
    StringT()
    {}

    explicit StringT(const char_type *str)
    {
        if (str != nullptr) {
            size_t len = strlen(str);
            m_str = std::make_unique<char_type[]>(len + 1);
            strcpy(m_str.get(), str);
        }
    }

    StringT(const StringT & other)
    {
        size_t len = 0;
        if (other.m_str)
            len = strlen(other.m_str.get());
        m_str = std::make_unique<char_type[]>(len + 1);
        strcpy(m_str.get(), other.m_str.get());
    }

    StringT(StringT && other) noexcept
    {
        m_str = std::move(other.m_str);
    }

    StringT & operator+=(const StringT &other)
    {
        if (other.m_str == nullptr)
            return *this;

        const size_t mysize{m_str ? strlen(m_str.get()) : 0};
        const size_t osize{strlen(other.m_str.get())};

        auto newStr = std::make_unique<char_type[]>(osize + mysize + 1);
        newStr[0] = '[=11=]';

        if (m_str)
            strcat(newStr.get(), m_str.get());
        strcat(newStr.get(), other.m_str.get());

        m_str = std::move(newStr);
        return *this;
    }

    size_t length() const
    {
        if (!m_str)
            return 0;
        return strlen(m_str.get());
    }

    friend
    std::ostream &operator<<(std::ostream &out, StringT<> &other)
    {
        if (other.m_str)
            out << other.m_str.get();
        return out;
    }

private:
    std::unique_ptr<char_type[]> m_str;
};

您会注意到此代码中没有对 new 或 delete 的调用。 m_str 将在需要时自行删除分配的内存。

Valgrind 发现了 3 个内存泄漏，但我不知道它们在哪里

Valgrind found 3 memory leaks but I can't figure out where they are

c++

valgrind